(1) Field of the Invention
This invention relates to the fabrication of integrated circuit devices and more particularly to a method of providing low contact resistance.
(2) Description of the Prior Art
In the existing process, either B or BF2 is used as an ion implantation source. Both of these ions have drawbacks. B+ implantation penetrates deeply and can cause a channel short after annealing where the channel is of very short length. BF2 implantation provides a shallow junction, but can cause heavy implant damage that is difficult to anneal out for low contact resistance. Sze in VLSI TECHNOLOGY published by McGraw-Hill Co. New York, N.Y. 1988 pages 350, 362 and 363 consider the advantages and problems of implantation of boron sources. Both boron ion species have been used separately for ion implantation, for example in U.S. Pat. No. 4,649,629 (Thomson-Mostek) and U.S. Pat. No. 4,764,478 (Toshiba).